discovery of planet pluto

Pluto nicknamed as “puzzling planet” or “runaway planet” was discovered by Clyde Tombaugh, a young US astronomer at the Arizona Lowell Observatory in 1930[footnoteRef:1]. Pluto is the largest known “dwarf planet” and the ninth largest object direct orbiting the sun. It’s the coldest, smallest and most distant planet from the sun. Similar to other Kuiper belt objects, the landscape of Pluto is mainly rock and ice.

Astronomers have remained puzzled with the origin of Pluto for centuries with earlier work suggesting that Pluto is a residual planetesimal. [1: Tombaugh, Clyde, and Patrick Moore. 1980. Out of the Darkness; The Planer Pluto. Harrisburg: Stackpole Book] There are varied hypothesis on Pluto’s origin such as the possible knocking out of Pluto by Neptune’s largest moon Triton implying that Pluto didn’t possess a fully planetary status.

The concept was later rejected as subsequent research established that there is no interaction of Neptune’s and Pluto’s orbits[footnoteRef:2]. Another strand of hypothesis argues that the formation of distant rocky core in the Sun’s protoplanetary disc resulted in the emergence of Pluto.  J. Hunter Waite Jr and Christopher Glein theory of the formation of Pluto referred to as Cosmo chemical model argue that Pluto is a giant comet containing gas and ice. According to Ley.

The discovery of Pluto dates back to early 19th Century with the discovery of Uranus by Sir William Herschel which was beyond Saturn that for centuries had been recognized as the outermost planet. Urbain Le Verrier’s exploration of the existence of Neptune following the perturbations identified in the Uranus orbit further increased the interest of exploration that led to the discovery of Pluto [footnoteRef:3].

Theorizing that the puzzling perturbations in Neptune and Uranus orbits, the founder of the famous Arizona Flagstaff Observatory Percival Lowell posited the existence of gravitational influence of an unknown planetary body, proposing the existence of a ninth planet named as Planet X. [2: Ley, Willy. 1956. The Demotion of Pluto. New York : Galaxy Publishing Corp.] [3: Tombaugh and Moore. 1980. ] Lowell search for Planet X began in 1903 but died in 1916 before finding Planet X after 13 years of dedication to mathematical theory and planet search.

Fortunately, Lowell had left sufficient work on the mathematical theory implying the remaining task is purely observational search. Having left a strong observatory team, the search for Planet X continued until the recording of an exceptional object on the search plates on 21st, 23rd, and 29th January and subsequently in February of 1930 by Tombaugh[footnoteRef:4].

Using the new astronomic technique of photographic plates integrated with a blink microscope, Tombaugh adopted a straightforward 2-3 days apart observation approach by using two images of a similar part of the sky looking for a moving star. Subsequently, Pluto was discovered to have five satellites; Charon (1978), Nix (2006), Hydra (2006), Kerberos (2013) and Styx 92013) with the largest being Charon which is half the size of Pluto[footnoteRef:5]. The discovery of Pluto attracted massive global interest resulting in over 1000 name suggestions.

There were varied suggestions for the name of Planet X including Lowell, Artemis, Indana, Atlas, Vulcan, Osiris, Zymal, Cronus, Apollos, Perseus, Erebus, Zeus, Idana, Bacchus, and Minerva. The suggestion of an 11-year-old schoolgirl in Oxford, Venetia Burney of after the god of the underworld was adopted which resulted in planet X named as Pluto. [4: Tombaugh, and Moore. 1980.

] [5: Stern, A., & Mitton, J., 2005, Pluto and Charon: Ice Worlds on the Ragged Edge of the Solar System, Wiley-VCH 1997] The dwarf planet is reported as one of the strangest yet interesting objects in the solar system. Given that Pluto takes 248-year-long, the planet is yet to complete, while a day in Pluto is equivalent to 153 hours, hence a day in Pluto is equivalent to 6.39 Earth Days. The planet’s diameter is 45% the diameter of Earth.

Pluto exhibits tilted 57 degrees and elliptical oval orbit around the sun which is unusual compared with other planets that follow circular orbits around the Sun. Although Pluto is on average 39 astronomical units away from the sun on average, oval-shaped orbit could position the planet 49.3 astronomical units from the sun implying that Pluto is periodically closer to the sun compared to Neptune. Between 1979 and 1999, Pluto was identified when close to the sun to be near perihelion implying that the Planet was closer to the sun than Neptune[footnoteRef:6].

It’s intriguing that even as Pluto’s and Neptune’s orbits appear to cross each other, the two orbits do not intersect implying that the two planets do not collide maintaining their stability despite their closeness. Contrary to another planet beyond mass that is characterized as gas giants, Pluto is rocky and small with a mass 1.31 x 1022 kilograms (0.22% Earth mass) and 0.5 billion cubic miles in volume (0.66%).

The low mass and size implies that Pluto’s density of 1.86 g/cm3 is 33.7% the density of the Earth [6: NASA Science. 2019.] Mountains, plains, valleys, and craters are the geological landscape of Pluto. Given that the temperatures in Pluto can be as low as -375 to -400 degrees Fahrenheit, the big blocks of water ice mountains can be as tall as two to three kilometers. The plains contain 98% nitrogen ice.

Some parts of the planet have 162 miles craters that have been experiencing signs of erosion suggesting resurfacing of tectonic forces in Pluto. The atmosphere in Pluto is tenuous and thin but expands and collapses depending on the planet location relative to the sun. Molecular nitrogen is the main atmosphere constituent which freezes and solidify to the extreme temperatures when the planet is far from the sun. The atmosphere freezes solid when Pluto is at perihelion, and the ice sublimates due to increased temperatures when the planet is at the aphelion.

Such atmospheric changes rule out the possibility of life existence of life in Pluto. The colors of Pluto are contrastively ranging from white, dark, charcoal black and orange. Pluto is located 3.7 billion miles (5.9 billion km, 39 astronomical units) from the sun implying that sunlight takes 5.5 hours to travel from the sun to Pluto, while it only takes 8.6 minutes for sunlight to travel from the sun to the Earth. The planet has a radius of 715 miles (1151 km) and a size equivalent to 1/6 of the Earth width.

Given Pluto’s great distance from the sun.